The invention relates to a display device comprising:
a photon source for emitting photons for a source image; the source comprising a plurality of pixels arranged in a surface;
an intermediate optical system for direction of the emitted photons;
a variable power optical system for modulating photon wavefront curvature from the intermediate optical system; and
a final optical system for directing photons from the variable power optical system into a user""s eye for viewing the source image with a perception of a changing image scene.
PCT Patent Specification No. WO99/08145 (Isis Innovation) describes such a display device. Such display devices operate to present source images to a user""s eyes so that the user has the perception of each source image pixel at any one of a continuum of distances. Applications of such a display device include investigation of the eye""s accommodative response and stereoscopic image display without conflict between accommodation and vergence.
A significant problem with optical systems for modulating photon wavefront curvature is due to the frequency and amplitude of optical element motion required. A display resolution of 1024xc3x97768 pixels refreshed (non-interlaced) at 60 Hz could require wavefront curvature to change at over 47 MHz. Mechanisms to translate or rotate optical elements at such frequencies by non-trivial amplitudes are bulky, expensive, and unreliable.
Optical systems exist which circumvent the problem of high-frequency translation and rotation. For example, they allow high-frequency deformation of reflective surfaces or high-frequency variation of the index of refraction of refractive surfaces. However there are other problems associated with these at present, including: their switching speeds are slowxe2x80x94of the order of kHz; they have relatively small diameters; their modes of wavefront deformation are limited; they have limited optical power; and they can have poor photon transmission.
Another problem relates to characteristics of pixels and their wavefronts. In order to realise many applications, some of which have been mentioned, the display should be capable of stimulating optically the eye""s accommodative system. This requires not only appropriate wavefront curvature, but also a sufficiency of photons at appropriate wavelengths and a sufficient diameter of exit pupil for each pixel.
Another problem is the aberration introduced by the optical system, especially if a wide field of view of the photon sources is required. A xe2x80x9cwide anglexe2x80x9d lens system can be used to reduce aberration across the field for a single, but not necessarily multiple, configurations of the device. A conventional xe2x80x9czoomxe2x80x9d lens system of varying optical power can be used to reduce aberrations for multiple configurations, but increases the mass of optical elements to be moved. A related problem is the overall mass of more complex systems, particularly if the device is to be used as a head-mounted display.
Display devices have been proposed which use the aforementioned non-rotating and non-translating optical systems to modulate wavefront curvature. However they do not overcome the problems outlined (especially the limitations of switching speed and diameter) in a practical, reliable, and cost-efficient manner, in order to simulate a wide field of view, high-resolution colour scene, with low aberration, in such a way as to stimulate optically the user""s accommodative system.
According to the invention, there is a display device comprising:
a photon source for emitting photons for a source image, the source comprising a plurality of pixels arranged in a surface;
an intermediate optical system for direction of the emitted photons;
a variable power optical system for modulating wavefront curvature of photons from the intermediate optical system; and
a final optical system for directing photons from the variable power optical system into a user""s eye for viewing the source image with a perception of a changing image scene;
characterised in that
the intermediate optical system comprises means for forming the photons into pencils, each pencil having photons from a single source pixel;
the variable power optical system is positioned with respect to the intermediate optical system such that the pencils converge towards one another;
the device further comprises a controller comprising means for receiving source image pixel co-ordinate data and intensity data, and data representing required perceived pixel distance, and for generating an output control signal for the variable power optical system, and an output control signal for the photon source, and
the variable power optical system comprises means for dynamically altering the wavefront curvature of the pencils in response to the control signal.
In one embodiment, the controller comprises means for presenting simultaneously all pixels that can be displayed with acceptable levels of aberration for a given state of the variable power optical system.
In another embodiment, the controller comprises means for ordering the sequence of pixel presentation such that the magnitude of variable power optical system state change is minimised.
In another embodiment, the intermediate optical system comprises a variable diameter aperture with two translational degrees of freedom, controlled by the controller.
In a further embodiment, the final optical system comprises a concave mirror.
In one embodiment, at least part of the intermediate optical system is positioned after the variable power optical system to direct the pencils to be parallel such that it is telecentric.
In another embodiment, the intermediate optical system has a wide field of view of the photon source, encompassing an area wider than its physical size.
In one embodiment, the controller comprises means for receiving inputs from an eye-tracking system for monitoring the look direction and accommodative state of the user, and for using said inputs when generating the control signal.
In another embodiment, the controller comprises means for receiving inputs from the scene synthesis system for estimating the look direction and accommodative state of the user, and for using said inputs when generating the control signal.
In one embodiment, the controller comprises means for receiving inputs from a wavefront sensor for monitoring the output of the variable power optical system, and for using said inputs when generating the control signal.